This invention relates to a leg restraint and, more particularly, to a novel assembly for protecting the legs of an occupant of an open-type ejection seat in an aircraft, when the occupant and the seat are ejected together from the aircraft into the surrounding airstream, i.e., an assembly for preventing injury due to windblast to the legs of the ejection seat occupant.
When an ejection seat and its occupant are ejected from an aircraft together, particularly at high speeds, the occupant is subjected to great pressure from the windblast. This situation is particularly dangerous if the occupant's limbs are caught in the windblast, because severe injury can result to the limbs. More specifically, and with regard to the occupant's legs during ejection and assuming that the ejection seat is stable, the aerodynamic pressure of the windblast bends the lower legs under the seat and lifts the upper legs. With the lower leg trapped under the seat pan, the lift forces on the upper leg must be carried by the knee joint as tension loads. Such tension loads are increased by drag forces acting on the feet and by the uncounterbalanced inertial response loads on the upper part of the lower leg. The inertial load is caused by the front panel of the seat bucket which traps the stagnated air behind the legs, and thereby cancels the action of the aerodynamic pressure on the front of the legs.
However, although ejection seat stability has been assumed, attitude instability (weakness or absence of tendency to align with the flight) of open-type ejection seats is well documented. A consequence of attitude instability is that aerodynamic forces may act on the legs over a wide range of angles-of-attack.
Accordingly, windblast safety protection for the legs requires: that the knees be relieved of the aerodynamic pressure induced tension loads which they bear during ejection; and that support for the legs against aerodynamic forces be available over a wide range of angles-of-attack. In addition, the windblast safety protection for the legs must be acceptable to the intended users, e.g., aircrew members, especially pilots. In turn, acceptance depends upon ease in donning and doffing, unencumberence to the user, lightness in weight, and undetectability while in use.